Structural identification and stabilization of the new high-temperature phases in A(III)–B(VI) systems (A = Ga, In, B = S, Se). Part 1: High-temperature phases in the Ga–S system

• Published in: Journal of alloys and compounds 2022-04, Vol.899, p.163264, Article 163264
• Main Authors: Volkov, V.V., Sidey, V.I., Naumov, A.V., Kolyshkin, N.A., Kosyakov, A.V., Nekrylov, I.N., Brezhnev, N. Yu, Zavrazhnov, A. Yu
• Format: Article
• Language: English
• Subjects: A(III)–B(VI)-Semiconductors; Composition; Crystal structure; Differential thermal analysis; Gallium sesquisulfide; High temperature; Lattice vacancies; Lattices; Phase diagrams; Phase diagrams of the Ga–S system; Phase transitions (polymorphism); Phases; Room temperature; Stabilization; Superstructures; Synchrotrons; Temperature; Thermal analysis; Transmission electron microscopy, TEM; X-ray diffraction
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.163264

•The self-consistency of thermal and structural data on Ga - S system was fulfilled.•The renewed T-x-diagram of the Ga–S system is obtained.•4 polymorphic modifications were found in the narrow range close to Ga2S3 composition.•The 2D-defect {111} planes in γ-Ga2+δS3 phase were observed with atomic resolution.•The relations between the family of polymorphic Ga2S3-structures were examined. [Display omitted] This article opens a series of publications devoted to the preparation and stabilization of new high-temperature (HT) semiconductor phases A (III) – B (VI), which have a large number of vacancies and possess a number of unique properties. In this first work from the proposed series, the T-x-diagram of the Ga–S system was investigated in the composition range x = (30.0–60.7) mol% S, and then the structural identification of new HT phases was carried out. For the Ga–S system, four polymorphic (α-, α′-, β-, γ-) Ga2S3 phases of different symmetry were found and displayed on the phase diagram near the Ga2S3 composition (x ∼ 60.0 mol% S). For the first time, it became possible to obtain in-situ a reliable direct proof for the existence of equilibrium in narrow temperature range for the re-opened cubic phase γ-Ga2+δS3 (x ≈ 59.0 mol% S), which was isolated at room temperature in a fairly pure form. We also confirmed the presence of another hexagonal β(α)-Ga2S3 modification, existing at much higher temperatures than the cubic γ-Ga2+δS3 phase. It was shown that the polymorphic α-Ga2S3 and α′-Ga2S3 phases mentioned in the literature form superstructures from the parent β-Ga2S3 phase. The observed structural variants for all four Ga2S3 polymorphic phases, containing up to 1/3 of vacancies in the Ga sub-lattices, are closely related to different methods of ordering Ga vacancies. The reliability of our studies follows from the combination of the methods used: differential thermal analysis (DTA), microstructural local analysis (TEM, HREM, SAED), powder X-ray diffractometry (XRD), including high-temperature synchrotron XRD.